The problem of dye transfer during laundry wash operations is common. There are two general mechanisms by which dyes are transferred during laundry washing. In the first method, certain dyes in colored fabrics tend to bleed directly into the wash solution. When the wash solution is agitated, these suspended dyes can be dispersed through the wash water and may eventually redeposit onto the surface of other fabrics in the wash solution. A common example of this phenomenon is the white garment turned pink after being washed with a red-colored garment. Another way whereby dyes are transferred in laundry wash solutions is for the dyes to bleed onto nearby areas of the same fabric. An example of this is the striped shirt or dress that, after laundering, has blended colors at the edges of the previously distinct stripes. Both of these highly undesirable results can be avoided by using a laundry detergent containing dye transfer inhibitors.
Dye transfer inhibitors are specialized compounds that are useful in preventing fabric dyes from redepositing or bleeding onto other fabrics. Dye transfer inhibitors can reduce dye transfer problems by complexing with suspended dyes to keep the dyes suspended in the wash solution, thereby preventing the dyes from redepositing once they leave the fabric surface. Dye transfer inhibitors may also function to prevent the initial bleeding of dyes from the fabrics. This not only reduces the undesired dye transfer problems but also helps preserve the color brightness of the fabrics over repeated washings.
Dye transfer inhibitors are generally organic polymers with melting points close to room temperature. Laundry detergent manufacturers usually incorporate dye transfer inhibitors into granular laundry detergents by spraying a viscous solution of dye transfer inhibitors onto the detergent granules near the end of the manufacturing process. However, there are several difficulties associated with dye transfer inhibitor spray-on procedures. First, spray-on can be expensive if special pumps are required to handle the viscous dye transfer inhibitor solutions. Second, excessive spray-on can make the granules sticky, causing the detergent granules to "gum up" into clumps which impede product flow. In addition to increasing manufacturing costs due to poor flow and handleability, clumps of sticky detergent are unappealing to consumers. Third, when sprayed, dye transfer inhibitors often give off an unpleasant odor which interferes with perfumes previously incorporated into the detergent granules. Fourth, control of the final product color is more difficult because certain dye transfer inhibitors turn pink in higher pH environments, thus necessitating the need to strictly control pH parameters in the spray-on step.
Thus, there has long been a need in the industry for an alternative process for manufacturing granular laundry detergents containing dye transfer inhibitors. Attempts to resolve the problems associated with spraying dye transfer inhibitors onto laundry detergent granules have largely involved variations in temperature, dye transfer inhibitor solution strength, and pH levels. These attempts, however, have failed to produce a dependable manufacturing process. Moreover, certain materials capable of functioning as dye transfer inhibitors, such as copolymers of N-vinylpyrrolidone and N-vinylimidazole, are explosive in dry, powdered form. Processes that avoid the messy spray-on procedures by employing these dry powders require costly equipment to safeguard against potentially dangerous explosions.
Accordingly, a new process that provides for a free-flowing dye transfer inhibiting detergent admix for addition to laundry detergent granules is desired. It is desired that the process for making the dye transfer inhibiting detergent admix be safe and cost-efficient. Furthermore, it is also desirable that such a process yield dye transfer inhibiting particles that are both aesthetically pleasing to the consumer and, when admixed with detergent granules, support a laundry product that is tinctured with a pleasant scent.